Multiband scheduling for wake up radio

ABSTRACT

Methods and systems for waking up a wireless receiving stations having wake-up radio (WUR) circuits. A method of providing a wake-up signal in a communications channel for a plurality of receiving stations, comprising: generating a plurality of series of waveform coded symbols, each series being incorporated into a respective wake-up-radio (WUR) frame that is intended for a respective receiving station and has a respective predefined bandwidth; combining the respective WUR frames into a multiband WUR data unit having a bandwidth that is greater than a sum of the predefined bandwidths of the wake-up radio frames; transmitting a wake-up signal including the multiband WUR data unit in the communications channel.

RELATED APPLICATIONS

The present application claims the benefit of and priority to U.S.Patent Appl. No. 62/486,607, filed Apr. 18, 2017, “MULTIBAND SCHEDULINGFOR WAKE UP RADIO”, which is incorporated herein by reference.

FIELD

The present application relates to methods and systems for communicatingwith multiple Wake Up Radio devices.

BACKGROUND

In wireless communication, efficient use of the available power is oneof the main goals of system design. Often, a wireless local area network(WLAN) device, such as in Internet of Things (IoT) applications, relieson a limited power supply (e.g., as supplied by rechargeable ornon-rechargeable batteries). Examples of such a device may includesensor devices located in remote fields measuring some physicalphenomenon, e.g., water level or temperature or location; and wearabledevices measuring some bodily function, e.g., pulse rate.

Such a device may be designed to operate on a low duty cycle (e.g.,communicating with an access point (AP) only once per day) and thus itmay not be appropriate for its WLAN receiver circuit to be always on.The limited power supply (e.g., battery) of the device may be quicklyexhausted if not provided with an appropriate sleep mode for the WLANreceiver circuit and an appropriate wake-up mechanism. The wake-upmechanism may require communication of wake-up signals between an AP anda device. In some applications, it may be desirable to enable an AP tocommunicate wake-up signals with multiple devices simultaneously in aspectrum efficient manner.

SUMMARY

According to a first aspect is a method of providing a wake-up signal ina communications channel for a plurality of receiving stations. Themethod includes generating a plurality of series of waveform codedsymbols, each series being incorporated into a respective wake-up-radio(WUR) frame that is intended for a respective receiving station and hasa respective predefined bandwidth. The respective WUR frames are thencombined into a multiband WUR data unit having a bandwidth that isgreater than a sum of the predefined bandwidths of the WUR frames. Awake-up signal including the multiband WUR data unit is transmitted inthe communications channel.

In some examples, the bandwidth of the multiband WUR data unit is 20MHz, each WUR frame has a bandwidth of 5 MHz or less, and a frequencyguard band is included between adjacent WUR frames. In some examples,the plurality of series of waveform coded symbols includes a firstseries incorporated into a first WUR frame that has a first predefinedbandwidth, a second series incorporated into a second WUR frame that hasa second predefined bandwidth, and a third series incorporated into athird WUR frame that has a third predefined bandwidth. Each waveformcoded symbol in the first series is generated from applying waveformcoding in time domain to a first OFDM waveform for which all subcarriersoutside of the first predefined bandwidth have been set to zero; eachwaveform coded symbol in the second series is generated from applyingwaveform coding in time domain to a second OFDM waveform for which allsubcarriers outside of the second predefined bandwidth have been set tozero; and each waveform coded symbol in the third series is generatedfrom applying waveform coding in time domain to a third OFDM waveformfor which all subcarriers outside of the third predefined bandwidth havebeen set to zero. In some examples, combining the respective WUR framesinto a multiband WUR data unit comprises adding the first, second andthird WUR frames.

In some example configurations, the first, second and third OFDMwaveforms are all generated from a 64 point IFFT and have a subcarrierspacing of 312.5 KHz and: the first OFDM waveform includes 14subcarriers within the first predefined bandwidth of which onesubcarrier is set to zero and thirteen subcarriers have a non-zerovalue; the second OFDM waveform includes 14 subcarriers within thesecond predefined bandwidth of which one subcarrier is set to zero andthirteen subcarriers have a non-zero value; and the third OFDM waveformincludes 14 subcarriers within the third predefined bandwidth of whichone subcarrier is set to zero and thirteen subcarriers have a non-zerovalue. In some examples, of the thirteen non-zero subcarriers of each ofthe first, second, and third OFDM waveforms, eight subcarriers are setto positive 1 and five subcarriers are set to negative 1.

In some examples, the first predefined bandwidth of the first OFDMwaveform includes the 14 subcarriers S₁₄ to S₂₇, in which a centralsubcarrier S₂₁ is set to zero, subcarriers S₁₅, S₁₆, S₁₉, S₂₂, S₂₄, S₂₅,S₂₆, and S₂₇ are set to plus one (+1); and subcarriers S₁₄, S₁₇, S₁₈,S₂₀, and S₂₂ are each set to negative one (−1); the second predefinedbandwidth of the second OFDM waveform includes the 14 subcarriers S⁻⁷ toS₆, in which a central subcarrier S₀ is set to zero, subcarriers S⁻⁶,S⁻⁴, S⁻³, S⁻², S⁻¹, S₁, S₄, and S₅ are set to plus one (+1); andsubcarriers S⁻⁷, S⁻⁵, S₂, S₃, and S₆ are each set to negative one (−1);and the third predefined bandwidth of the third OFDM waveform includesthe 14 subcarriers S⁻²⁸ to S⁻¹⁵, in which a central subcarrier S⁻²¹ isset to zero, subcarriers S⁻²⁸, S⁻²⁶, S⁻²⁵, S⁻²², S⁻²⁰, S⁻¹⁸, S⁻¹⁶, andS⁻¹⁵ are set to plus one (+1); and subcarriers S⁻²⁷, S⁻²⁴, S⁻²³, S⁻¹⁹,and S⁻¹⁷ are each set to negative one (−1).

In some examples, the first predefined bandwidth, second predefinedbandwidth, and third predefined bandwidth are each less that 4.1 MHz, aguard band of 2.5 MHz is included between the first WUR frame and thesecond WUR frame, and a guard band of 2.5 MHz is included between thesecond WUR frame and the third WUR frame.

In some examples, each of the waveform coded symbols represents arespective data bit and comprises a guard interval followed by first andsecond sub-symbols of equal duration, the corresponding data bit beingrepresented by a different relative energy distribution between thefirst and second sub-symbols. The data bits may be coded using on-offkeying to represent data “1” and data “0” bits.

In some examples, the multiband WUR data unit is appended to a legacypreamble symbol.

In some examples, the method includes transmitting a notification toeach of the receiving stations indicating the predefined bandwidth ofthe WUR frame intended for the receiving station. In some examples themethod includes receiving the wake-up signal at one of the receivingstations, the reviving station filtering the wake-up signal toselectively receive the predefined bandwidth of the WUR frame intendedfor the receiving station.

According to another aspect is a method for receiving the wake-up signalprovided according to the method of the first aspect, comprisingfiltering the wake-up signal to selectively receive one of thepredefined WUR frame bandwidths.

According to a further aspect is a transmitter for providing a wake-upsignal in a communications channel, comprising a waveform coding moduleconfigured to provide a wake-up signal according to the above describedmethod.

According to a further aspect is a station for receiving a wake-upsignal provided according to the method of the first aspect, the stationincluding a filter for filtering the wake-up signal to selectivelyreceive the predefined bandwidth of the WUR frame intended for thereceiving station.

According to another aspect is a method and receiver for receiving awake-up signal transmitted according to the aspects and embodimentssummarized above.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made, by way of example, to the accompanyingdrawings which show example embodiments of the present application, andin which:

FIG. 1 is a block diagram illustrating communications between an AP andan example station having a Wake Up Radio circuit;

FIG. 2 is a block diagram illustrating communications between an AP andmultiple stations having respective Wake Up Radio circuits;

FIG. 3 illustrates a multiband frame format for an example wake-up radiodata unit;

FIG. 4 is a block diagram illustrating a multiband wake-up frameencoding system according to an example embodiment;

FIG. 5A shows frequency domain and time domain representations of anexample first sub-band waveform used in the system of FIG. 4;

FIG. 5B shows frequency domain and time domain representations of anexample second sub-band waveform used in the system of FIG. 4;

FIG. 5C shows frequency domain and time domain representations of anexample third sub-band waveform used in the system of FIG. 4; and

FIG. 6 is a block diagram illustrating a multiband wake-up framedecoding wake up receiver circuits.

Similar reference numerals may have been used in different figures todenote similar components.

DETAILED DESCRIPTION

A user device or station such as a machine type communication device orsensor device that is intended to operate in a wireless network such asa wireless local area network (WLAN) may have a separate low-power WakeUp Radio (WUR) circuit in addition to a higher power WLAN transceivercircuit. A WUR circuit is generally a low-power receiver circuitdesigned for receiving and detecting a wake-up signal, and may in someexamples be a simplified version of the main WLAN transceiver circuitand may be implemented on an integrated circuit (IC) or chip. The WURcircuit communicates with the WLAN transceiver circuit, or otherequivalent circuit, of the device, so the WLAN transceiver circuit maysleep and conserve power until the WUR circuit wakes up the WLANtransceiver circuit. The WUR circuit wakes up the WLAN transceivercircuit, or other equivalent circuit, when the WUR circuit detects awake-up signal from an access point AP (typically, an AP associated withthe WLAN device).

In this regard, FIG. 1 is a schematic diagram illustrating an example AP102 and an example station 104 associated with the AP 102. In exampleembodiments the station 104 is a low duty cycle WLAN device or otherwireless device. The example station 104 includes a WLAN transceivercircuit 106 (e.g., a Wi-Fi transceiver) and a WUR circuit 108. The AP102 includes WLAN transceiver circuit 110. In example embodiments, theWUR circuit 108 is a simple low power receiver that does not have atransmitter and functions to wake up the WLAN transceiver circuit 106when needed.

FIG. 1 illustrates a set of example signals that may be communicated forwaking up a sleeping WLAN transceiver circuit 106. The AP 102 may send awake-up signal 152, carrying a Wake-Up-Radio (WUR) data unit 200(described further below) to the station 104. The WUR data unit 200 isdetected by the WUR circuit 108, and the WUR circuit 108 sends aninternal wake-up signal 154 to the WLAN receiver circuit 106, waking upthe WLAN transceiver circuit 106 if the WLAN receiver circuit 106 is insleep mode. The WLAN transceiver circuit 106 then sends an ACK signal156 back to the AP 102. Appropriate information exchange 158 between theAP 102 and the station 104 (via the WLAN transceiver circuit 106) maythen take place. After the information exchange 158 is finished, theWLAN transceiver circuit 106 may return to the sleep state.

Although FIG. 1 shows wakeup signal 152 being communicated to a WURcircuit 108 that is associated with a WLAN transceiver circuit 106, theprocesses and systems described in the present disclosure may beapplicable to other circuits, including other wireless receivercircuits, which may benefit from a wake-up mechanism.

In some applications, including for example IoT applications, densepopulations of stations 104 may be serviced by small numbers of APs 102and thus example embodiments are described herein which facilitatemultiband communications for WUR signals that allow a single AP 102 tosend unique WUR frames using the same data unit 200 to multiple stations104. In this regard, FIG. 2 shows a wakeup signal 152 that includesmultiband WUR data unit 200 being communicated simultaneously to threestations 104-1, 104-2, 104-3 that each include a respective WUR circuit108.

An example frame format for a multiband WUR data unit 200 is shown inFIG. 3. The heights of the various blocks shown in FIG. 3 illustrate therelative bandwidths (BWs) of each portion. In the example of FIG. 3, theWUR data unit 200 includes a legacy preamble 210 pre-pended to amultiband WUR unit 201. Legacy preamble 210 is included to silencelegacy devices within the network and may be omitted in some exampleswhere legacy equipment is not anticipated to operate. In applicationswhere legacy preamble 210 is omitted, WUR Data Unit 200 will beidentical to multiband WUR unit 201. Multiband WUR unit 201 includesthree concurrent WUR frames 250-1, 250-2 and 250-3 (also referred togenerically as WUR frame 250), each of which can include uniqueinformation for a respective one of the stations 104-1, 104-2 and 104-3.In example embodiments, legacy preamble 210 occupies a channel bandwidth(CH BW) of 20 MHz, and each of the WUR frames 250-1, 250-2 and 250-3occupy a respective unique 4.1 MHz sub-band BW-1, BW-2 and BW-3 of thechannel bandwidth CH BW. In the illustrated embodiment, adjacent WURFrames 250-1 and 250-2 are separated in frequency by a guard band GB andadjacent WUR Frames 250-2 and 250-3 are also separated in frequency byfurther guard band GB. Furthermore, in the illustrated embodiment, anedge band EB is provided at the outer frequency boundary of WUR frame250-1 and a similar edge band EB is provided at the outer frequencyboundary of WUR frame 250-3.

As will be explained in greater detail below, in example embodiments theMultiband WUR Unit 201 is derived from a conventional 802.11 OrthogonalFrequency Division Multiplexing (OFDM) symbol having the numerologyparameters: Number of subcarriers (tones)=64; useful symbol durationT_(u)=3.2 μs; subcarrier spacing SS=312.5 KHz; and Bandwidth=20 MHz. Inexample embodiments, fourteen (14) subcarriers are allocated for each ofthe WUR Frames 250-1, 250-2, 250-3, seven (7) subcarriers are allocatedfor each guard band GB and four (4) subcarriers are allocated for eachedge band EB such that the allocation of the 64 subcarriers can berepresented as in the following table:

TABLE 1 Allocation of 64 subcarriers in multiband WUR Unit 201:Subcarrier Nos. Allocated To Band Width S₂₈ to S₃₁ (4 tones) EB 1406.25KHz S₁₄ to S₂₇ (14 tones) WUR Frame 250-1 (BW-1) 4062.5 KHz S₇ to S₁₃ (7tones) GB 2500 KHz S₋₇ to S₆ (14 tones) WUR Frame 250-2 (BW-2) 4062.5KHz S₋₁₄ to S₋₈ (7 tones) GB 2500 KHz S₋₁₅ to S₋₂₈ (14 tones) WUR Frame250-3 (BW-3) 4062.5 KHz S₋₃₂ to S₋₂₉ (4 tones) EB 1406.26 KHz

Each WUR frame 250-1, 205-2, 250-3 includes information that can bespecific for the respective stations 104-1, 104-2 and 104-3, and eachWUR frame 250-1, 250-2 and 250-3 can include the following fields:WUR-Reference Signal field 252; WUR signal (SIG) field 254; MAC header262; frame body 264; and frame check sequence (FCS) 266. In an exampleembodiment WUR-Reference Signal field 252 may include a wakeup signalpreamble, for example a pseudo noise (PN) sequence. The WUR signal (SIG)field 254 may include a control signal. The MAC header 262 may include areceiver address. The MAC header 262, frame body 264 and FCS 266 maytogether be referred to as the payload of the WUR frame 250. In someexamples, WUR frames 250-1, 250-2 and 250-3 may omit one or more of theframe fields identified in FIG. 3, and/or may include additional fields.

The WUR-Reference Signal 252 is provided for packet detection andsynchronization. In some examples, WUR-Reference signal 252 may includea short training field (STF) that can be used by the WUR circuit 108 inthe respective station 104-1, 104-2, 104-3 to detect the WUR frame 250as distinct from other frames and allow the WUR circuit 108 tosynchronize to the WUR frame 250. In some examples, WUR-Reference Signal252 may include a sequence that can be correlated at the WUR circuit 108to facilitate frame synchronization.

In example embodiments, the WUR circuit 108 of each of the stations104-1, 104-2 and 104-3 is implemented as a simple low power consumingreceiver circuit, and accordingly WUR frame 250 is designed to enableefficient and accurate decoding at a low power WUR circuit 108. In thisregard, time-domain waveform coding (WFC) is used for parts of the WURFrame 250 that follow the WUR Reference Signal 252, shown in FIG. 3 asWFC Coded Portion 268. In example embodiments filtering is applied atthe WUR circuits 108 of respective stations 104-1, 104-2 and 104-3 toseparate the respective WUR Frames 205-1, 250-2 and 205-3 from themultiband WUR Unit 201. Typically, increasing the filter coefficient(e.g. number of taps) at a filter increases the accuracy of thefiltering which is beneficial in a multiband environment, however italso increases cost and complexity of the filter. Furthermore,simulations have indicated that in some examples of a WFC signal, thegreater the number of taps used in a filter at the WUR circuit 108 thegreater the chance of inter-symbol interference occurring is.Accordingly, example embodiments are described herein that may in someapplications provide a multiband waveform coded WUR Frame format thatcan be decoded at WUR receivers using filters with a filter coefficientthat optimizes the trade-offs between inter-symbol interference (ISI),power consumption and adjacent band interference.

FIG. 4 is a basic system block diagram illustrating a WUR system thatemploys waveform coding. FIG. 4 shows the process flow applied at the APtransceiver 110 to generate multiband WUR unit 201 with the format shownin Table 1 above. Each of the processing blocks 300, 304-1, 304-2,304-3, 306, 307 and 308 shown as being performed at AP transceiver 110represents an operation that may for example be implemented as a moduleor element as part of one or more integrated circuits.

In the example of FIG. 4, unique source data is provided for each of thestations 104-1, 104-2 and 104-3 in the form of binary on-off keying(OOK) mapped source data 280-1, 280-2, and 280-3 respectively. Inexample embodiments, the source data 280-1, 280-2, and 280-3 includesbits for encoding and inclusion in the WFC coded portions 268 of the WURFrames 250-1, 250-2 and 250-3, respectively. The AP transceiver 110implements parallel processing paths 285-1, 285-2 and 285-3 for therespective source data 280-1, 280-2, and 280-3.

The operation of first processing path 285-1 as it processes and encodesOOK mapped source data 280-1 and outputs corresponding WUR Frame 250-1will now be described in greater detail. In some examples, source data280-1 is segmented into groups of K bits for processing. Forward errorcorrection (FEC) encoding to apply error correction and/or compress data(e.g. encoding K bits to J bit codewords) can be applied to the binarydata by an FEC encoding operation 300, however such encoding may beomitted in some embodiments.

The processing path 285-1 includes a waveform source 304-1 that providessymbol waveforms 410-1 to a waveform coding operation 306. Symbolwaveform 410-1 has a predefined energy configuration within a predefinedbandwidth (BW) and a predefined symbol duration (T_(u)) that includes apredefined number of samples (N). As will now be described, in exampleembodiments symbol waveform 410-1 is a multi-carrier waveform derivedfrom subcarriers S₁₄ to S₂₇ generated from a 64 point IFFT. In thepresently described example, waveform source 304-1 includes memory 305that stores a previously generated time domain version of an OrthogonalFrequency Division Multiplexing (OFDM) waveform such as the example timedomain symbol waveform 410-1 that is shown in FIG. 5A. In particular, inan example embodiment an OFDM waveform generator 301-1 that includes a64 point inverse fast Fourier transform (IFFT) operation is used togenerate a frequency domain OFDM symbol 402-1 in which the sub-set ofallocated subcarriers S₁₄ to S₂₇ that occupy the bandwidth BW-1 are usedto provide symbol waveform 410-1.

In the illustrated example symbol 402-1 of FIG. 5A, the centralsubcarrier S₂₁ in the group of 14 subcarriers S₁₄ to S₂₇ is a Null, andthe remaining 13 subcarriers in the group are assigned values asfollows: Subcarriers S₁₅, S₁₆, S₁₉, S₂₂, S₂₄, S₂₅, S₂₆, and S₂₇ are setto plus one (+1); and subcarriers S₁₄, S₁₇, S₁₈, S₂₀, and S₂₂ are eachset to negative one (−1). The remaining subcarriers S⁻³² to S⁻¹³ and S₂₈to S₃₁ are each set to 0. In the illustrated example, the symbol 402-1is derived from a conventional 802.11 OFDM symbol having the numerologyparameters noted above in respect of Table 1: Number of subcarriers=64,with number of used subcarriers SC_(u)=14 (including subcarriers S₁₄ toS₂₇, with S₂₁ used for a null); useful symbol duration T_(u)=3.2 μs; andsubcarrier spacing SS=312.5 KHz. The bandwidth BW-1 of symbol 402-1 is13×312.5 Khz≈4.1 MHz. Waveform 410-1 in FIG. 5A represents a time domainversion of OFDM symbol 402-1. In example embodiments, OFDM time domainwaveform 410-1 is generated using the standard 802.11 sampling rate of20 MHz, such that OFDM waveform 410-1 includes N=64 samples.

As noted above, in example embodiments the operations performed by OFDMsymbol generator 301-1 to provide symbol waveform 410-1 are done at aconfiguration time prior to WUR frame 250-1 processing and transmission,with waveform source 304-1 then providing successive copies of thepre-stored symbol waveform 410-1 at the time of WUR frame 250-1generation by AP Tx/Rx 110, thus eliminating the requirement for an IFFToperation for each symbol waveform used for WUR frame 250-1. In at leastsome example embodiments, OFDM waveform generator 301-1 is configurableand can be used to generate symbol waveforms that have differentnumerology parameters than those stated above, such that the storedwaveform can be changed if required.

In the example of FIG. 4, a waveform coding operation 306 is used tocode the J data bits encoded from OOK source data 280-1 onto Jsuccessive time-domain symbol waveforms 410-1. In an example embodiment,the waveform coding that is applied at operation 306 is Manchestercoding, which is also known as phase encoding (PE). In particular,Manchester coding is a line code in which the encoding of each data bitis either low then high, or high then low, of equal time. Accordingly,at waveform coding operation 306, waveform 410-1 is effectively dividedinto two sub-symbols of equal duration (T_(u)/2) with each “0” bit isencoded as a set of two sub-symbols and, each “1” bit is encoded as setof two sub-symbols. In an example embodiment, the encoding is as shownin Table 2 below:

TABLE 2 Manchester encoding of OOK data bits: OOK First sub-symbolSecond sub-symbol Data Bit SUB₁ SUB₂ “1” 1 (ON) 0 (OFF) “0” 0 (OFF) 1(ON)

It will be appreciated that the sub-symbol order described herein can bereversed for data bits 0 and 1 in alternative configurations.

In example embodiments, an “OFF” sub-symbol includes substantially blankor zero energy, and an “ON” sub-symbol includes a higher energy levelthan the “OFF” sub-symbol. In example embodiments, the “ON” sub-symbolenergy matches the energy of a corresponding duration of the symbolwaveform 410-1 having the same duration as the “ON” sub-symbol. Waveformcoding operation 306 applies the PE coding to the symbol waveform 410-1in the time domain, and in this regard, FIG. 5A graphically illustrates,in time domain the coding that is applied to OFDM symbol waveform 410-1to generate a data “1” WFC symbol 520-1 and a data “0” WFC symbol 520-0(referred to generically as WFC symbol 520).

In an example embodiment, a guard interval (GI) is prepended to each WFCsymbol 510 as part of waveform coding operation 306. In one example, theGI has a duration T_(gi)=0.8 μs (e.g. ¼ of useful symbol duration T_(u))such that each WFC symbol 520 has a duration T_(tot)=T_(u)+T_(GI)=4 μs.In example embodiments, guard interval GI is created by prepending zeroenergy samples such that the WFC symbols 520 have no or negligibleamplitude for the duration T_(gi), which may boost the transmitterenergy for the portions of the symbol that are included in the usefulsymbol duration T_(u). In particular, transmitter energy per symbol isfixed to a set amount that is determined either by power spectraldensity regulation or a power amplifier of the transmitter, andaccordingly the less energy used for the GI the more energy can be usedfor the non-zero “ON” sub-symbol portion.

In some example embodiments the standard 802.11 sampling rate of 20 MHzis applied by waveform coding operation 306 when generating the datasymbols 520. Accordingly, in the case of a Data “1”, the waveform codedoutput symbol 520-1 has a duration of T_(tot)=4 μs and L=80 samples andincludes, in the following order: a guard interval of durationT_(gi)=0.8 μs that includes M=16 samples that correspond to GI samplesof waveform 350; a first sub-symbol SUB₁ of duration T_(u)/2=1.6 μs thatincludes N/2=32 samples copied from the portion of symbol waveform 350that follows the GI portion; and a second sub-symbol SUB₂ of durationT_(u)/2=1.6 μs that includes N/2=32 samples in which the subcarrierenergy has been forced to “0”. In the example shown in FIG. 5A, thesymbol 520-1 has negligible or zero energy except during the durationbetween T_(gi) and T_(u)/2+T_(gi) (namely 0.8 μs to 2.4 μs)

In the case of data “0” output symbol 520-0, the GI portion remains thesame and the order of sub symbols SUB₁ and SUB₂ is reversed such that inthe case of a Data “0”, the waveform coded output symbol 520-0 has aduration of T_(tot)=4 μs and L=80 samples and includes, in the followingorder: a guard interval of duration T_(gi)=0.8 μs that includes M=16samples that correspond to GI samples of waveform 350; a firstsub-symbol SUB₁ of duration T_(u)/2=1.6 μs that includes N/2=32 samplesin which the subcarrier energy has been forced to “0”; and a secondsub-symbol SUB₂ of duration T_(u)/2=1.6 μs that includes N/2=32 samplescopied from final 32 samples of symbol waveform 350. In the exampleshown in FIG. 5A, the symbol 520-1 has negligible or zero energy exceptduring the duration between T_(u)/2+T_(gi) to T_(tot) (namely 2.4 μs to4 μs).

Accordingly, in example embodiments each of the J data bits from OOKsource data 280-1 is represented at the output of waveform codingoperation 306 as a respective WFC symbol 520. Each WFC symbol 520 has adefined total symbol duration T_(tot) that corresponds to L samples.Each WFC symbol 520 includes two components, namely: a leading GI thathas a leading guard interval duration T_(gi) that corresponds to Msamples; and a useful symbol component immediately following the GI andhaving a useful symbol duration T_(u) that corresponds to N samples. Theuseful symbol of duration T_(u) is divided into two sub-symbols SUB₁ andSUB₂ that each have equal length durations T_(u)/2 corresponding to N/2samples. Binary bit information is represented by the two sub-symbolsSUB₁ and SUB₂ being either low then high, or high then low. The actualsignal value contained in the GI is immaterial, however, as noted above,using a low or zero energy signal can boost transmitter energy innon-zero regions of the symbol. In example embodiments the WFC Symbol520 is configured to fall within a defined BW with minimal leakage,facilitating the use of a low tap filter at WUR circuit 108 of Station104-1.

It will be appreciated that WFC symbols 520 having the characteristicsstated in the previous paragraph could be generated using methods,components and symbol numerology other than those described in respectof the system shown in FIG. 4. Furthermore, in some example embodimentscopies of WFC symbols 520-0 and 520-1 can be pre-generated and stored inmemory 305 at waveform source 304, with wave form coding operation 306selecting the appropriate WFC symbol to output based on the OOK value ofan OOK source data 280-1.

Accordingly, in example embodiments, each set of K OOK source data bits280-1 is represented at the output of waveform coding operation 306 as aseries of J WFC symbols 520 that form WFC portion 268-1. WUR-REF Signal252-1 is then prepended to the WFC portion 268-1 to complete WUR Frame250-1.

Processing path 285-2 processes and encodes OOK mapped source data 280-2to output corresponding WUR Frame 250-2 in a manner identical to thatdescribed above in respect of processing path 285-1 except that thewaveform source 304-2 uses a different set of OFDM subcarriers forfrequency domain waveform 402-2 and time domain waveform 410-2 asillustrated in FIG. 5B. In particular, OFDM waveform generator 301-2applies a 64 point inverse fast Fourier transform (IFFT) operation togenerate a frequency domain OFDM symbol 402-2 in which the sub-set ofallocated subcarriers S⁻⁷ to S₆ that occupy the bandwidth BW-2 are usedto provide symbol waveform 410-2. In the illustrated example symbol402-2 of FIG. 5B, the central subcarrier S₀ in the group of 14subcarriers S⁻⁷ to S₆ is a DC Null, and the remaining 13 subcarriers inthe group are assigned values as follows: Subcarriers S⁻⁶, S⁻⁴, S⁻³,S⁻², S⁻¹, S₁, S₄, and S₅ are set to plus one (+1); and subcarriers S⁻⁷,S⁻⁵, S₂, S₃, and S₆ are each set to negative one (−1). The remainingsubcarriers S⁻³² to S⁻⁸ and S₇ to S₃₁ are each set to 0. The bandwidthBW-2 of symbol 402-2 is 13×312.5 Khz≈4.1 MHz. Waveform 410-2 in FIG. 5Brepresents a time domain version of OFDM symbol 402-2.

Processing path 285-3 processes and encodes OOK mapped source data 280-3to output corresponding WUR Frame 250-3 in a manner identical to thatdescribed above in respect of processing paths 285-1 and 285-2 exceptthat the waveform source 304-3 uses a different set of OFDM subcarriersfor frequency domain waveform 402-3 and time domain waveform 410-3 asillustrated in FIG. 5C. In particular, OFDM waveform generator 301-3applies a 64 point inverse fast Fourier transform (IFFT) operation togenerate an frequency domain OFDM symbol 402-3 in which the sub-set ofallocated subcarriers S⁻²⁸ to S⁻¹⁵ that occupy the bandwidth BW-3 areused to provide symbol waveform 410-3. In the illustrated example symbol402-3 of FIG. 5C, the central subcarrier S⁻²¹ in the group of 14subcarriers S⁻²⁸ to S⁻¹⁵ is a Null, and the remaining 13 subcarriers inthe group are assigned values as follows: Subcarriers S⁻²⁸, S⁻²⁶, S⁻²⁵,S⁻²², S⁻²⁰, S⁻¹⁸, S⁻¹⁶, and S⁻¹⁵ are set to plus one (+1); andsubcarriers S⁻²⁷, S⁻²⁴, S⁻²³, S⁻¹⁹, and S⁻¹⁷ are each set to negativeone (−1). The remaining subcarriers S⁻³² to S⁻²⁹ and S⁻¹⁴ to S₃₁ areeach set to 0. The bandwidth BW-3 of symbol 402-3 is 13×312.5 Khz≈4.1MHz. Waveform 410-3 in FIG. 5C represents a time domain version of OFDMsymbol 402-3.

As noted above, the WFC symbols included in WUR frames 250-1, 250-2 and250-3 are each derived from a respective group of sub-carriers from a 64carrier OFDM symbol. In some examples, OFDM waveform generators 301-1,301-2, 301-3 are implemented using different subcarrier groups of thesame 64-subcarrier OFDM waveform generator. In example embodiments, thetone patterns used within each of the OFDM symbols 402-1, 402-2 and402-3 are based on the corresponding tones that are occupied in theconventional OFDM 802.11 Long Training Sequence (LTS) symbol (with theexception of OFDM symbol 402-3 where the +1 subcarrier S⁻²⁸ and −1subcarrier S⁻²⁷ values have been added because the correspondingsubcarriers S⁻²⁸ and S⁻²⁷ are null in the conventional LTS symbol). Inthe illustrated embodiment, each of the OFDM symbols 402-1, 402-2 and402-3 includes eight (8) sub-carriers set to positive one (+1) and five(5) sub-carriers set to negative one (−1). However, in alternativeembodiments different tone patterns could be employed.

Accordingly, the processing paths 285-1, 285-2 and 285-3 respectivelyoutput signals concurrently in three different frequency bands asfollows: processing path 285-1 outputs WUR frame 250-1 in frequency bandBW-1; processing path 285-2 outputs WUR frame 250-2 in frequency bandBW-2; and processing path 285-3 outputs WUR frame 250-3 in frequencyband BW-3. The three WUR frames 250-1, 250-2 and 250-3 are combined atadding circuit 307 in a synchronized sample-by-sample manner using thesame sampling rate that was used in generating WFC symbols 520 togenerate multiband WUR unit 201. Multiband WUR unit 201 has thecharacteristics described above in respect of FIG. 3 and Table 1. Inexamples where legacy preamble 210 is included, the legacy preamble 210is prepended to multiband WUR unit 201 to form WUR data unit 200, whichis then upconverted at modulator 308 to a channel carrier frequency andtransmitted through wireless network channel 410 as part of wake-upsignal 152. In example embodiments the same transmit filter used for802.11 is used to provide spectral filtering to ensure that thetransmitted symbols, including any edge tones, fall within a 20 MHzspectral mask.

FIG. 6 shows three target stations 104-1, 104-2 and 104-3 and thedecoding operations performed at three respective WUR circuits 108 inrespect of a WUR data unit 200 included in a wake-up signal 152 receivedthrough wireless channel 410. In some examples, each processing block310, 312, 314, 316, 318 and 320 shown as being performed at WUR circuit108 represents an operation that may be implemented as a module orelement that is part of one or more integrated circuits. As shown inFIG. 6, each of the stations 104-1, 104-2 and 104-3 includes arespective filter 312-1, 312-2 and 312-3 (referred to generically asfilter 312). In at least some examples, the receiving stations 104-1,104-2 and 104-3 have been pre-configured or pre-informed during priorcommunications of the WUR Frame 250-1, 250-2, or 250-3 that has beenallocated to it, enabling each station 104-1, 104-2, 104-3 to tune itsrespective filter 312-1, 312-2, 312-3 of its respective WUR circuit 108to the bandwidth of its allocated WUR Frame 250-1, 250-2 or 205-3.Accordingly, in an example embodiment: station 104-1 configures itsfilter 312-1 as a band pass filter for BW-1, which corresponds to a 6.56MHz center frequency with a 4 MHz bandwidth; station 104-2 configuresits filter 312-2 as a low pass filter for BW-2, which corresponds to a 0MHz center frequency with a 4 MHz bandwidth; and station 104-3configures its filter 312-3 as a band pass filter for BW-3, whichcorresponds to a −6.56 MHz center frequency with a 4 MHz bandwidth. Insome examples the filters 312 are 8 tap filters (filter coefficient=8)to optimize between inter-band interference rejection and ISI. In someexamples the filters are 4 tap filters (filter coefficient=4) tooptimize between inter-band interference rejection and ISI, but with agreater weighting to reduced power consumption.

The processing of a received WUR data unit 200 at the WUR circuit 108 ofstation 104-1 will now be described in greater detail according to anexample embodiment. The received WUR data unit 200 is received as partof wake-up signal 152 at WUR circuit 108 and down converted at modulator310 to baseband. The baseband WUR data unit 200 is then filtered atfilter 312-1 to restrict the signal to the bandwidth BW-1 thatcorresponds to WUR frame 250-1. Synchronization operation 314 thenprocesses the received WUR frame 250-1 to synchronize to the symbolboundaries of the WFC symbols 520 that are included in the recovered WFCportion 268-1R of the WUR frame 250-1. In this regard, in some exampleembodiments synchronization operation 314 relies on WUR-Reference Signal252 in received WUR frame 250-1 to allow WUR circuit 108 to synchronizesample timing to the incoming symbol boundaries of individual recoveredWFC symbols 520 that are included within recovered WFC coded portion268-1, enabling each of the recovered WFC symbols 520 to be sequentiallyprocessed by energy detection operation 316 and hard decision operation318. In example embodiments, prior to or as an initial step in the powerdetection operation 316, the prepended GI is removed from the WFC symbol520 being processed. The power detection operation 316 then measures thepower distribution in each of first and second sub-symbols SUB₁ andSUB₂. By way of example, in one embodiment, power detection operation316 is configured to sample the WFC symbol 520 at the same frequencyused at waveform coding operation 306 (for example the conventional 20MHz of 802.11) and process the WFC symbol 520R as follows: the first Msamples (corresponding to duration T_(gi)) are discarded; an averagepower distribution value is determined for the next N/2 samples(corresponding to a duration of T_(u)/2) which represent sub-symbolSUB₁; and a further average power distribution value is determined forthe next N/2 samples (corresponding to a duration of T_(u)/2) whichrepresent sub-symbol SUB₂. In the example of a 20 MHz sampling rate andtotal symbol time of T_(tot)=4 μs the discarded GI includes M=16samples, and first sub-symbol SUB₁ and second sub-symbol SUB₂ eachinclude N/2=32 samples.

Decision block 318 is configured to compare the average powerdistribution values between the first and second sub-symbols SUB₁ andSUB₂ and make a corresponding data “0” or “1” decision. In theillustrated example, if the magnitude of the average power distributionvalue is greater in the first sub-symbol SUB₁ than the second sub-symbolSUB₂, then the received WFC symbol 520 is decoded as a data “1”; and ifthe average power magnitude value is greater in the second sub-symbolSUB₂ than the first sub-symbol SUB₁, then the received WFC symbol 520 isdecoded as a data “0”. The successive data bits from decision operation318 are assembled to provide recovered FEC OOK data, with FEC decodingoperation 320 being applied to generate recovered OOK source data 280-1Rthat corresponds to original OOK source data 280-1. The recovered OOKsource data 280-1R may for example contain information and instructionsfor internal wake-up signal 154 for the main WLAN transceiver circuit106 of station 104-1.

Stations 104-2 and 104-3 are similarly configured to recover theirrespective OOK source data 280-2R and 280-3R from the WUR data unit 200.

Although the WUR data unit 200 is shown as having three concurrent WURFrames 250-1, 250-2, 250-3 appended to legacy preamble 210, the dataunit 200 may include more or less than three WUR frames. In someembodiments, the number of WUR frames appended to legacy preamble 210may be configurable. In some embodiments the bandwidth of the WUR framesand guard bands between them, and their frequency assignment within thebandwidth of legacy preamble 210, could be configurable. In some exampleembodiments, each WUR frame may have a bandwidth of 5 MHz or less.

The present disclosure may provide certain example algorithms andcalculations for implementing examples of the disclosed methods andsystems. However, the present disclosure is not bound by any particularalgorithm or calculation.

Although the present disclosure may describe methods and processes withsteps in a certain order, one or more steps of the methods and processesmay be omitted or altered as appropriate. One or more steps may takeplace in an order other than that in which they are described, asappropriate.

Although the present disclosure may be described, at least in part, interms of methods, a person of ordinary skill in the art will understandthat the present disclosure is also directed to the various componentsfor performing at least some of the aspects and features of thedescribed methods, be it by way of hardware components, software or anycombination of the two.

The present disclosure may be embodied in other specific forms withoutdeparting from the subject matter of the claims. The described exampleembodiments are to be considered in all respects as being onlyillustrative and not restrictive. Selected features from one or more ofthe above-described embodiments may be combined to create alternativeembodiments not explicitly described, features suitable for suchcombinations being understood within the scope of this disclosure.

All values and sub-ranges within disclosed ranges are also disclosed.Also, although the systems, devices and processes disclosed and shownherein may comprise a specific number of elements/components, thesystems, devices and assemblies could be modified to include additionalor fewer of such elements/components. For example, although any of theelements/components disclosed may be referenced as being singular, theembodiments disclosed herein could be modified to include a plurality ofsuch elements/components. The subject matter described herein intends tocover and embrace all suitable changes in technology.

The invention claimed is:
 1. A method of providing a wake-up signal in acommunications channel for a plurality of receiving stations,comprising: generating a plurality of series of waveform coded symbolsincluding a first series incorporated into a first wake-up-radio (WUR)frame that has a first predefined bandwidth, a second seriesincorporated into a second WUR frame that has a second predefinedbandwidth, and a third series incorporated into a third WUR frame thathas a third predefined bandwidth, each of the first, second, and thirdWUR frame being intended for a respective receiving station; combiningthe first, second and third WUR frames into a multiband WUR data unit ina synchronized sample-by-sample manner using a same sampling rate thatwas used in generating each of the first, second, and third WUR frames,wherein the multiband WUR data unit has a bandwidth that is greater thana sum of the predefined bandwidths of the WUR frames; and transmitting awake-up signal including the multiband WUR data unit in thecommunications channel, wherein each waveform coded symbol in the firstseries is generated from applying waveform coding in time domain to afirst orthogonal frequency division multiplexing (OFDM) waveform forwhich all subcarriers outside of the first predefined bandwidth havebeen set to zero; wherein each waveform coded symbol in the secondseries is generated from applying waveform coding in time domain to asecond OFDM waveform for which all subcarriers outside of the secondpredefined bandwidth have been set to zero; and wherein each waveformcoded symbol in the third series is generated from applying waveformcoding in time domain to a third OFDM waveform for which all subcarriersoutside of the third predefined bandwidth have been set to zero.
 2. Themethod of claim 1 wherein the bandwidth of the multiband WUR data unitis 20 MHz, each WUR frame having a bandwidth of 5 MHz or less, wherein afrequency guard band is included between adjacent WUR frames.
 3. Themethod of claim 2 wherein the method further comprises upconverting themultiband WUR data unit provide the wake-up signal.
 4. The method ofclaim 3 wherein the first, second and third OFDM waveforms are allgenerated from a 64 point IFFT and have a subcarrier spacing of 312.5KHz, wherein the first OFDM waveform includes 14 subcarriers within thefirst predefined bandwidth of which one subcarrier is set to zero andthirteen subcarriers have a non-zero value; wherein the second OFDMwaveform includes 14 subcarriers within the second predefined bandwidthof which one subcarrier is set to zero and thirteen subcarriers have anon-zero value; and wherein the third OFDM waveform includes 14subcarriers within the third predefined bandwidth of which onesubcarrier is set to zero and thirteen subcarriers have a non-zerovalue.
 5. The method of claim 4 wherein of the thirteen non-zerosubcarriers of each of the first, second, and third OFDM waveforms,eight subcarriers are set to positive 1 and five subcarriers are set tonegative
 1. 6. The method of claim 5 wherein: the first predefinedbandwidth of the first OFDM waveform includes the 14 subcarriers S₁₄ toS₂₇, in which a central subcarrier S₂₁ is set to zero, subcarriers S₁₅,S₁₆, S₁₉, S₂₂, S₂₄, S₂₅, S₂₆, and S₂₇ are set to plus one (+1); andsubcarriers S₁₄, S₁₇, S₁₈, S₂₀, and S₂₂ are each set to negative one(−1); the second predefined bandwidth of the second OFDM waveformincludes the 14 subcarriers S⁻⁷ to S₆, in which a central subcarrier S₀is set to zero, subcarriers S⁻⁶, S⁻⁴, S⁻³, S⁻², S⁻¹, S₁, S₄, and S₅ areset to plus one (+1); and subcarriers S⁻⁷, S⁻⁵, S₂, S₃, and S₆ are eachset to negative one (−1); and the third predefined bandwidth of thethird OFDM waveform includes the 14 subcarriers S⁻²⁸ to S⁻¹⁵, in which acentral subcarrier S⁻²¹ is set to zero, subcarriers S⁻²⁸, S⁻²⁶, S⁻²⁵,S⁻²², S⁻²⁰, S⁻¹⁸, S⁻¹⁶, and S⁻¹⁵ are set to plus one (+1); andsubcarriers S⁻²⁷, S⁻²⁴, S⁻²³S⁻¹⁹, and S⁻¹⁷ are each set to negative one(−1).
 7. The method of claim 3 wherein the first predefined bandwidth,second predefined bandwidth, and third predefined bandwidth are eachless than 4.1 MHz, a guard band of 2.5 MHz is included between the firstWUR frame and the second WUR frame, and a guard band of 2.5 MHz isincluded between the second WUR frame and the third WUR frame.
 8. Themethod of claim 1 wherein each of the waveform coded symbols representsa respective data bit and comprises a guard interval followed by firstand second sub-symbols of equal duration, the corresponding data bitbeing represented by a different relative energy distribution betweenthe first and second sub-symbols.
 9. The method of claim 8 wherein thedata bits are coded using on-off keying to represent data “1” and data“0” bits, wherein a data “1” bit is represented by a waveform codedsymbol with the first sub-symbol having higher energy than the secondsub-symbol, and a data “0” bit is represented by a waveform coded symbolwith the first sub-symbol having lower energy than the secondsub-symbol.
 10. The method of claim 8 wherein the data bits are codedusing on-off keying to represent data “1” and data “0” bits, wherein adata “0” bit is represented by a waveform coded symbol with the firstsub-symbol having higher energy than the second sub-symbol, and a data“1” bit is represented by a waveform coded symbol with the firstsub-symbol having lower energy than the second sub-symbol.
 11. Themethod of claim 8 wherein the guard interval of each waveform codedsymbol has substantially zero energy.
 12. The method of claim 8 whereineach waveform coded symbol has a duration of 4 μs, each guard intervalhas a duration of 0.8 μs, and each sub-symbol has a duration of 1.6 μs.13. The method of claim 1 wherein the multiband WUR data unit isappended to a legacy preamble symbol.
 14. The method of claim 11comprising transmitting a notification to each of the receiving stationsindicating the predefined bandwidth of the WUR frame intended for thereceiving station.
 15. A transmitter for transmitting a wake-up signalin a communications channel, comprising: a waveform coding moduleconfigured to generate a multiband wake-up-radio (WUR) data unitincluding a plurality of WUR frames each of which is intended for arespective receiving station, the plurality of WUR frames including afirst WUR frame that incorporates a first series of waveform codedsymbols and has a first predefined bandwidth within a bandwidth of themultiband WUR data unit, a second WUR frame that incorporates a secondseries of waveform coded symbols and has a second predefined bandwidthwithin the bandwidth of the multiband WUR data unit, and a third WURframe that incorporates a third series of waveform coded symbols and hasa third predefined bandwidth within the bandwidth of the multiband WURdata unit, wherein the multiband WUR data unit is generated in asynchronized sample-by-sample manner using a same sampling rate that wasused in generating each of the first, second, and third WUR frames; anda modulator for up-converting the multiband WUR data unit onto a carrierfrequency and transmitting a wake-up signal including the multiband WURdata unit in the communications channel; the bandwidth of the WUR dataunit being greater than a sum of the predefined bandwidths of the WURframes, wherein each waveform coded symbol in the first series isgenerated from applying waveform coding in time domain to a firstorthogonal frequency division multiplexing (OFDM) waveform for which allsubcarriers outside of the first predefined bandwidth have been set tozero; wherein each waveform coded symbol in the second series isgenerated from applying waveform coding in time domain to a second OFDMwaveform for which all subcarriers outside of the second predefinedbandwidth have been set to zero; and wherein each waveform coded symbolin the third series is generated from applying waveform coding in timedomain to a third OFDM waveform for which all subcarriers outside of thethird predefined bandwidth have been set to zero.
 16. The transmitter ofclaim 15 wherein the bandwidth of the multiband WUR data unit is 20 MHz,the predefined bandwidth of each WUR frame is 5 MHz or less, and thewaveform coding module is configured to include a frequency guard bandbetween adjacent WUR frames and edge bands at edge frequencies of thebandwidth of the multiband WUR data unit.
 17. The transmitter of claim15 wherein the OFDM subcarriers have subcarrier spacing of 312.5 KHz,and wherein the OFDM subcarriers within each of the first, second andthird predefined bandwidths include 14 subcarriers of which onesubcarrier is set to zero and thirteen subcarriers that have a non-zerovalue.
 18. The transmitter of claim 17 wherein of the thirteen non-zerosubcarriers of each of the first, second, and third OFDM waveforms,eight subcarriers are set to positive 1 and five subcarriers are set tonegative
 1. 19. A method for receiving a wake-up signal comprising:down-converting and filtering the received wake-up signal to select oneof a first, second, and third predefined bandwidth, wherein the receivedwake-up signal includes a multiband wake-up-radio (WUR) data unit havinga plurality of WUR frames each of which is intended for a respectivereceiving station, the plurality of WUR frames including a first WURframe that incorporates a first series of waveform coded symbols and hasthe first predefined bandwidth within a bandwidth of the multiband WURdata unit, a second WUR frame that incorporates a second series ofwaveform coded symbols and has the second predefined bandwidth withinthe bandwidth of the multiband WUR data unit, and a third WUR frame thatincorporates a third series of waveform coded symbols and has the thirdpredefined bandwidth within the bandwidth of the multiband WUR dataunit, wherein the multiband WUR data unit being generated in asynchronized sample-by-sample manner using a same sampling rate that wasused in generating each of the first, second, and third WUR frames;wherein each waveform coded symbol in the first series is generated fromapplying waveform coding in time domain to a first orthogonal frequencydivision multiplexing (OFDM) waveform for which all subcarriers outsideof the first predefined bandwidth have been set to zero; wherein eachwaveform coded symbol in the second series is generated from applyingwaveform coding in time domain to a second OFDM waveform for which allsubcarriers outside of the second predefined bandwidth have been set tozero; wherein each waveform coded symbol in the third series isgenerated from applying waveform coding in time domain to a third OFDMwaveform for which all subcarriers outside of the third predefinedbandwidth have been set to zero; and decoding the waveform coded symbolsincorporated in the WUR frame that occupies the selected predefined WURframe bandwidth.
 20. The method of claim 19 where decoding the waveformcoded symbols comprises determining a bit value for each waveform codedsymbol based on a relative energy distribution between sub-symbols ofthe waveform coded symbol.
 21. The method of claim 19 wherein thefiltering is performed at a filter having a filtering coefficient of atleast 4 and less than or equal to
 8. 22. A wake-up radio receivercircuit comprising: a modulator configured to down convert a receivedwake-up signal to a baseband signal that includes a multibandwake-up-radio (WUR) data unit having a plurality of WUR frames that eachincorporate a series of waveform coded symbols intended for a respectivereceiving station, each WUR frame occupying a respective predefinedbandwidth within a bandwidth of the multiband WUR data unit; a filterconfigured to filter the baseband signal to select one of the predefinedWUR frame bandwidths; and energy detection and decision operationsconfigured to determine, based on a relative energy distribution betweensub-symbols of each waveform coded symbol, bit values for the waveformcoded symbols incorporated in the WUR frame that occupies the selectedpredefined WUR frame bandwidth.
 23. The wake-up radio receiver circuitof claim 22 wherein the filter has a filtering coefficient of at least 4and less than or equal to 8.